Phosphoric acid concentration



Oct. 29, 1968 c, o wm 3,408,168

PHOSPHORIC ACID CONCENTRATION Filed July 16, 1965 2 Sheets-Sheet lINVENTOR.

' M/LLA/PD a. GODWl/V Oct. 29, 1968 M. c. GODWIN 3,408,168

PHOSPHORIC ACID CONCENTRATION Filed July 16, 1965 2 Sheets-Sheet 2 mvsrv r01? M/LLARD 6. GODW/N United States Patent 3,408,168 PHOSPHORICACID CONCENTRATION Millard C. Godwin, Lakeland, Fla., assignor, by mesneassignments, to Armour Agricultural Chemical Company, a corporation ofDelaware Filed July 16, 1965, Ser. No. 472,410 3 Claims. (Cl. 23-307)ABSTRACT OF THE DISCLOSURE Submerged combustion concentration ofphosphoric acid wherein water instead of phosphoric acid is introducedinto the dehydrator vessel in starting up the process. When operatingconditions are reached addition of water is stopped and phosphoric acidintroduced into the vessel while withdrawing the water.

This invention relates to phosphoric acid concentration, and moreparticularly to method and apparatus for the concentration of wetprocess phosphoric acid in which hot combustion gases are employed asthe heating medium.

In the dehydration of wet process phosphoric acid in which combustiongases are discharged through a dip pipe into a pool of phosphoric acidheld within a bricklined dehydrator vessel, it is found that in thestart-up stage an oft-condition product caused by trying of the aci isproduced, and also there is a tendency for metal salt deposits to buildup on the dip pipe.

I have discovered that water, instead of acid, can be utilized duringthe start-up period, and thereby the startup time is shortened, theamount of cit-condition product is greatly reduced, while at the sametime the salt deposit build-up on the evaporator surfaces issubstantially eliminated for this period. By using the water technique,it is found that there is no plugging during the start-up period.

A primary object, therefore, is to provide a process for overcoming theabove described difliculties in the start-up of the dehydration of wetprocess phosphoric acid. Another object is to provide a process in whichwater is utilized in the start-up of the dehydration operation to reducestart-up time, production of off-condition product, and build-up of saltdeposits on evaporator surfaces. Other specific objects and advantageswill appear as the specification proceeds.

The invention is shown in an illustrative embodiment by the accompanyingdrawings, in Which- FIGURE 1 is a diagrammatic and part-sectional viewof apparatus which may be employed in the practice of the invention;FIG. 2, a top plan view on an enlarged scale of the evaporator vesselwith the upper top portion of the vessel removed; and FIG. 3, a verticalsectional view of the structure shown in FIG. 2.

In the illustration given, particularly in FIG. 1, designates a furnaceor combustion chamber. A suitable fuel gas, such as propane, isintroduced from a source of supply through pipe 11, and air isintroduced through pipe 12 from a blower. The gases enter a vortexburner 13 and are discharged into the combustion chamber through pipe14.

15 designates a dehydration vessel which, like combustion chamber 10, isprovided with an inner carbon brick lining. On one side is provided amanhole opening 16 closed by a manhole cover 16a. The insulation withinthe dehydrator provides a dehydrator well 17, and in line with the upperportion of the Well 17 is a drawofi pipe 18 from which the dehydratedphosphoric acid is recovered. In the upper portion of the dehydratorvessel is a vapor pipe 19. The moisture-laden gases which dis- "iceengage from the acid in the space above the evaporator bottom areremoved by the duct 19 to a separator 20 Where entrained acid dropletsare removed and may be returned through pipe 21 to the product receiver.The gases continue on to the floating bed scrubber 22 where condensableand water-soluble pollutants are removed.

In the evaporator 15, the well 17 is in the form of an arc, and a seriesof four dip pipes 23 depend from the elongated combustion chamber 10 andare provided with end pipes 24 extending downwardly into the well 17, asseen best in FIG. 2.

If desired, the metal sleeve 25 of each dip pipe may be provided on theinterior thereof with a ceramic lining 26. The upper end of each metalstrip 25 may be embedded within a top layer 27 of ceramic material.Thus, the metal of the dip pipe may be protected with a thick layer ofceramic on the interior thereof. The lower short length of pipe 24 iskept cool because of its proximity to the liquid in the well, beingwashed and cooled by the liquid during the dehydration operation. Thepresent process, however, may be operated with or without the ceramiclinings.

In the specific structure shown, wet process phosphoric acid to bedehydrated is fed into the well 17 through inlet pipes 28, and betweenthe acid inlet pipes are water withdrawal pipes 29 (three in number) asseen best in FIG. 2. Pipe 30 may be employed as a thermocouple tube.

OPERATION In the operation of the process, I introduce water through theinlet pipes 28 into the arcuate well 17 while at the same time bringingabout a combustion of the fuel gases with air and discharging the heatedgases through the four dip pipes 23 into the arcuate well 17. Theoperation is continued, putting in enough water to have some overflow,to bring the gas heater to proper on-stream condition, while protectingthe brick lining. The water serves the function of keeping theevaporator cool during the period in which the furnace or combustionchamber is brought to full flow rates of gas and air and to a watertemperature of about 200 F. When such conditions have been attained,feed phosphoric acid is then introduced through the pipes 28 at fullfeed rate, and simultaneously the water is drained through pipes 29 andequilibrium is thus quickly attained. The operator can observe theliquid being withdrawn and can detect the point at which acid isbeginning to flow from the vessel and can then terminate the withdrawalof water. The process is then continued in the usual way. Moisture-ladengases disengage from the liquid within the dehydrator and are carriedoff through the pipe 19, while dehydrated or concentrated phosphoricacid is drawn oif through pipe 18 to a product receiver.

Specific examples illustrative of the apparatus and process may be setout as follows:

Example I The process was carried out in apparatus as shown in thedrawings but instead of starting up the apparatus with Wet processphosphoric acid, water was introduced through a period of about 2 hours,and with a constant overflow. The water was introduced through pipes 28,and the gas heater or furnace 10 was brought up gradually until theair-diluted gases from the furnace were about 1900 F. and with full flowrates of gas and air. The temperature of the water was about 200 F. andsteam passed through the vapor lines. After full operating on-streamconditions for gas and air were reached, the fiow of water wasdiscontinued and Wet process phosphoric acid analyzing 55.4 percent P 0and 4.8 percent solids was introduced at full rate through the pipes 28.

Waterwas withdrawn through pipes 29 until the acid filled the Well andequilibrium was then quickly reached. The lining brick suffered nodamage. The acid was dehydrated at a pool temperature of around 600 F.and an excellent product was obtained with substantially nooil-condition product. There were no metal salt deposits during thestart-up period.

Example II The above process was repeated in apparatus similar to thatshown in the drawings except that the ceramic liner was omitted. By theuse of the water feed, build-up of deposits was avoided during thestart-up period, and the build-up of deposit did not begin until afterthe acid at full flow rate was introduced into the dehydrator. There wassubstantially no off-condition product and no build-up of salt depositsduring the start-up operation.

While in the foregoing specification I have set forth specific structureand procedure in considerable detail for the purpose of illustratingembodiments of my invention, it will be understood that such details maybe varied widely by those skilled in the art without departing from thespirit of my invention.

I claim:

1. In the dehydration of Wet process phosphoric acid in which hotcombustion gases are discharged through a dip pipe into a dehydratorvessel containing wet process phosphoric acid, the improvementcomprising starting up the process using water in said dehydrator vesselinstead of phosphoric acid, continuing the operation until combustionoperating temperatures and gas flow rates are reached, discontinuing thefeeding of water to said vessel,

and feeding Wet process phosphoric acid to said vessel while drainingwater from the vessel.

2. The process of claim 1 in which the wet process phosphoric acid isfed at full flow rate into the vessel While draining the water.

3. In the dehydrationof wet process phosphoric acid in which hotcombustion gases are discharged through a dip pipe into a dehydratorvessel containing wet process phosphoric acid, the improvementscomprising starting up the process by introducing water into thedehydrator vessel in contact with said hot combustion gases, maintainingan overflow of Water from said vessel until the gas and air mixtureforming said combustion gases are brought to about operating flow ratesand temperatures, discontinuing the feeding of water, and feeding wetprocess phosphoric acid into said vessel while draining water from thevessel.

References Cited UNITED STATES PATENTS 3,073,683 1/1963 Switzer 23307 X3,104,947 9/1963 Switzer 23307 X 3,276,510 10/1966 Austin 23165 X OTHERREFERENCES Young et a1.: Wet-Process Phosphoric Acid, ChemicalEngineering Progress, vol. 59, #12, December 1963, pp. to 84.

NORMAN YUDKOFF, Primary Examiner. S. EMERY, Assistant Examiner.

